1. Field of the Invention
The present invention is broadly concerned with improved diets for oral administration comprising intact, non-hydrolyzed, non-digested, naturally occurring protein(s) supplemented with a minor amount of an additive selected from the group consisting of di- and tripeptides having at least one essential amino acid residue. More particularly, it is concerned with such diets, and corresponding feeding methods, wherein the presence of di- or tripeptide additive results in greater utilization of amino acid nitrogen by the animal, allowing corresponding reductions in the protein content of the diets.
2. Description of the Prior Art
Presently, most essential amino acids supplied by animal diets are derived from naturally occurring plant or animal proteins. It is known, however, to supplement normal diets with various free amino acids such as lysine from lysine.sup.. HCl, DL-methionine, L-tryptophan, L-isoleucine and L-threonine. The theory of such supplementation is that the free amino acids are thought to be absorbed by an animal more readily than more complex peptides and proteins. For example, the addition of lysine.sup.. HCl to a ton of swine finishing feed allows the dietary protein content to be reduced from 14% to 12%, by replacing 100 pounds of soybean meal with 97 pounds of corn and 3 pounds of lysine.sup.. HCl.
Peptides can be produced by enzymatic digestion of protein with proteinases or peptidases. Typically, the digestive process involves the enzymatic degradation of dietary proteins to free amino acids or peptides of varying chain lengths. Research has been conducted in the past to evaluate the nutritional value of dietary peptide supplements in the form of protein hydrolysate peptides, which are a mixture of many amino acids found in proteins prior to hydrolysis thereof. Such experiments have been carried out in many species, including man and rodents. Additionally, studies have been carried out in many species to evaluate the absorptive potential and mechanism of utilization for amino acids and peptides, including man, rodents, fowl, ruminants, and several aquatic species. These studies involve infusion of peptides into the digestive system of the test species, or in vitro digestive investigations.